It is inherent in the nature of sovereignty not to be amenable to the suit of any individual without its consent. This is the general sense and the general practice of mankind; and the exemption, as one of the attributes of sovereignty, is now enjoyed by the government of every State in the Union. . . . The contracts between a nation and individuals are only binding on the conscience of the sovereign, and have no pretensions to a compulsory force. They confer no right of action, independent of the sovereign will. To...authorize suits against States for the debts they owe...could not be done without waging war against the contracting State..., a power which would involve such a consequence, would be altogether forced and unwarranted.